Method and device for transmitting control information in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system. More particularly, the present invention relates to a method for executing a CSI report in a wireless communication system, and a device therefor, the method comprising the steps of: composing a CSI report set having a first serving cell and a second serving cell, wherein each of the serving cells includes a plurality of independently consisting subframe subsets; receiving, at the predetermined subframe, a PDCCH signal requesting an aperiodic CIS report on the CSI report set; transmitting a PUSCH signal including a first CSI on the corresponding subframe subset in the first serving cell and a second CSI on the corresponding subframe subset in the second serving cell, wherein the first CSI and the second CSI are calculated on the basis of the subframe subset given by a predetermined method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2012/001605, filed on Mar. 5, 2012, which claims the benefit of U.S. Provisional Application Ser. No. 61/448,664, filed on Mar. 3, 2011, the contents of which are all hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and, more specifically, to a method and device for transmitting control information. The wireless communication system can support carrier aggregation (CA).

BACKGROUND ART

Wireless communication systems have been widely deployed to provide various types of communication services including voice and data services. In general, a wireless communication system is a multiple access system that supports communication among multiple users by sharing available system resources (e.g. bandwidth, transmit power, etc.) among the multiple users. The multiple access system may adopt a multiple access scheme such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), or Single Carrier Frequency Division Multiple Access (SC-FDMA).

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies in a method for efficiently transmitting control information in a wireless communication system and a device for the same. Another object of the present invention is to provide a channel format, signal processing scheme and device for the same for efficiently transmitting control information. Another object of the present invention is to provide a method for efficiently allocating resources for transmitting control information and a device for the same.

The technical problems solved by the present invention are not limited to the above technical problems and those skilled in the art may understand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing a method for reporting channel state information (CSI) in a wireless communication system, the method including: configuring a CSI report set including a first serving cell and a second serving cell, each serving cell including a plurality of independently configured subframe subsets; receiving, in a predetermined subframe, a physical downlink control channel (PDCCH) signal requesting an aperiodic CIS report on the CSI report set; and transmitting a physical uplink shared channel (PUSCH) signal including first CSI on the corresponding subframe subset in the first serving cell and second CSI on the corresponding subframe subset in the second serving cell, wherein the first CSI and the second CSI are calculated on the basis of a subframe subset given by a predetermined method.

In another aspect of the present invention, provided herein is a communication device configured to report channel state information (CSI) in a wireless communication system, including: a radio frequency (RF) unit; and a processor, wherein the processor is configured to configure a CSI report set including a first serving cell and a second serving cell, each serving cell including a plurality of independently configured subframe subsets, to receive, in a predetermined subframe, a physical downlink control channel (PDCCH) signal requesting an aperiodic CIS report on the CSI report set, and to transmit a physical uplink shared channel (PUSCH) signal including first CSI on the corresponding subframe subset in the first serving cell and second CSI on the corresponding subframe subset in the second serving cell, wherein the first CSI and the second CSI are calculated on the basis of a subframe subset given by a predetermined method.

When the predetermined subframe belongs to different subframe subsets in the CSI report set, the first CSI and the second CSI may be calculated based on the same subframe subset as a subframe subset to which the predetermined subframe belongs in a serving cell in which the PDCCH signal is received.

The plurality of subframe subsets may include two subframe subsets. When the PDCCH signal is received in the first serving cell, the first CSI may be calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI may be calculated based on a subframe subset different from the subframe subset to which the predetermined subframe belongs in the first serving cell.

The PDCCH signal may include a 1-bit subframe subset indicator, and at least one of the first CSI and the second CSI may be calculated based on a subframe subset indicated by the subframe subset indicator.

When the PDCCH signal is received in the first serving cell, the first CSI may be calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI may be calculated based on the subframe subset indicated by the subframe subset indicator.

The plurality of subframe subsets may include two subframe subsets. When the PDCCH signal is received in the first serving cell, the first CSI may be calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI may be calculated based on a subframe subset different from a previously reported subframe subset.

Advantageous Effects

According to the present invention, control information can be efficiently transmitted in a wireless communication system. Furthermore, a channel format, signal processing scheme and device for the same for efficiently transmitting control information can be provided. In addition, it is possible to efficiently allocate resources for transmitting control information.

The effects of the present invention are not limited to the above-described effects and other effects which are not described herein will become apparent to those skilled in the art from the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings:

FIG. 1 illustrates physical channels used in a 3GPP LTE system and a signal transmission method using the same;

FIG. 2 illustrates a radio frame structure;

FIG. 3 illustrates a resource grid of a downlink slot;

FIG. 4 illustrates an uplink subframe structure;

FIGS. 5 and 6 illustrate slot level structures of PUCCH formats 2/2a/2b;

FIG. 7 illustrates an uplink signal processing procedure;

FIG. 8 illustrates SC-FDMA and OFDMA;

FIG. 9 illustrates a signal processing procedure for mapping DFT process output samples to a single carrier in clustered SC-FDMA;

FIGS. 10 and 11 illustrate a signal processing procedure of mapping DFT process output samples to multiple carriers in clustered SC-FDMA;

FIG. 12 illustrates a signal processing procedure in segmented SC-FDMA;

FIG. 13 illustrates a concept of management of downlink component carriers in a base station (BS);

FIG. 14 illustrates a concept of management of uplink component carriers in a user equipment (UE);

FIG. 15 illustrates a concept of management of multiple carriers by one MAC layer in a BS;

FIG. 16 illustrates a concept of management of multiple carriers by one MAC layer in a UE;

FIG. 17 illustrates a concept of management of multiple carriers by one MAC layer in a BS;

FIG. 18 illustrates a concept of management of multiple carriers by multiple MAC layers in a UE;

FIG. 19 illustrates a concept of management of multiple carriers by multiple MAC layers in a BS;

FIG. 20 illustrates a concept of management of multiple carriers by one or more MAC layers in a UE;

FIG. 21 illustrates channel state information generation and transmission;

FIG. 22 illustrates a CQI reporting scheme of LTE;

FIG. 23 illustrates a procedure of processing UL-SCH data and control information;

FIG. 24 illustrates multiplexing control information and UL-SCH data on a PUSCH;

FIG. 25 illustrates a heterogeneous network including a macro cell and a micro cell;

FIG. 26 illustrates a method for eliminating inter-cell interference in a heterogeneous network;

FIG. 27 illustrates a configuration of a restricted subset and an aperiodic CSI report in a single carrier situation;

FIG. 28 illustrates operation of a UE to perform aperiodic CSI reporting in a heterogeneous network supporting carrier aggregation (CA);

FIG. 29 illustrates aperiodic CSI reporting according to one embodiment of the present invention; and

FIG. 30 illustrates configurations of a BS and a UE applicable to the present invention.

BEST MODE

Embodiments of the present invention are applicable to a variety of wireless access technologies such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), and Single Carrier Frequency Division Multiple Access (SC-FDMA). CDMA can be implemented as a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can be implemented as a radio technology such as Global System for Mobile communications (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA can be implemented as a radio technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wireless Fidelity (Wi-Fi)), IEEE 802.16 (Worldwide interoperability for Microwave Access (WiMAX)), IEEE 802.20, Evolved UTRA (E-UTRA). UTRA is a part of Universal Mobile Telecommunications System (UMTS). 3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA, employing OFDMA for downlink and SC-FDMA for uplink. LTE-Advanced (LTE-A) is an evolution of 3GPP LTE. While the following description is given, centering on 3GPP LTE/LTE-A to clarify the description, this is purely exemplary and thus should not be construed as limiting the present invention.

In a wireless communication system, a UE receives information from a BS through downlink (DL) and transmits information to the BS through uplink (UL). Information transmitted/received between the UE and BS includes data and various types of control information, and various physical channels are present according to type/purpose of information transmitted/received between the UE and BS.

FIG. 1 illustrates physical channels used in a 3GPP LTE system and a signal transmission method using the same.

When powered on or when a UE initially enters a cell, the UE performs initial cell search involving synchronization with a BS in step S101. For initial cell search, the UE is synchronized with the BS and acquire information such as a cell Identifier (ID) by receiving a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) from the BS. Then the UE may receive broadcast information from the cell on a Physical Broadcast Channel (PBCH). In the mean time, the UE may determine a downlink channel status by receiving a Downlink Reference Signal (DL RS) during initial cell search.

After initial cell search, the UE may acquire more specific system information by receiving a Physical Downlink Control Channel (PDCCH) and receiving a Physical Downlink Shared Channel (PDSCH) based on information of the PDCCH in step S102.

The UE may perform a random access procedure to access the BS in steps S103 to S106. For random access, the UE may transmit a preamble to the BS on a Physical Random Access Channel (PRACH) (S103) and receive a response message for preamble on a PDCCH and a PDSCH corresponding to the PDCCH (S104). In the case of contention-based random access, the UE may perform a contention resolution procedure by further transmitting the PRACH (S105) and receiving a PDCCH and a PDSCH corresponding to the PDCCH (S106).

After the foregoing procedure, the UE may receive a PDCCH/PDSCH (S107) and transmit a Physical Uplink Shared Channel (PUSCH)/Physical Uplink Control Channel (PUCCH) (S108), as a general downlink/uplink signal transmission procedure. Here, control information transmitted from the UE to the BS is called uplink control information (UCI). The UCI may include a Hybrid Automatic Repeat and request Acknowledgement/Negative-ACK (HARQ ACK/NACK) signal, a scheduling request (SR), channel state information (CSI), etc. The CSI includes a channel quality indicator (CQI), a precoding Matrix Index (PMI), a rank indicator (RI), etc. While the UCI is transmitted through a PUCCH in general, it may be transmitted through a PUSCH when control information and traffic data need to be simultaneously transmitted. The UCI may be aperiodically transmitted through a PUSCH at the request/instruction of a network.

FIG. 2 illustrates a radio frame structure. In a cellular OFDM wireless packet communication system, uplink/downlink data packet transmission is performed on a subframe-by-subframe basis. A subframe is defined as a predetermined time interval including a plurality of OFDM symbols. 3GPP LTE supports a type-1 radio frame structure applicable to FDD (Frequency Division Duplex) and a type-2 radio frame structure applicable to TDD (Time Division Duplex).

FIG. 2( a) illustrates a type-1 radio frame structure. A downlink subframe includes 10 subframes each of which includes 2 slots in the time domain. A time for transmitting a subframe is defined as a transmission time interval (TTI). For example, each subframe has a length of 1 ms and each slot has a length of 0.5 ms. A slot includes a plurality of OFDM symbols in the time domain and includes a plurality of resource blocks (RBs) in the frequency domain. Since downlink uses OFDM in 3GPP LTE, an OFDM symbol represents a symbol period. The OFDM symbol may be called an SC-FDMA symbol or symbol period. An RB as a resource allocation unit may include a plurality of consecutive subcarriers in one slot.

The number of OFDM symbols included in one slot may depend on Cyclic Prefix (CP) configuration. CPs include an extended CP and a normal CP. When an OFDM symbol is configured with the normal CP, for example, the number of OFDM symbols included in one slot may be 7. When an OFDM symbol is configured with the extended CP, the length of one OFDM symbol increases, and thus the number of OFDM symbols included in one slot is smaller than that in case of the normal CP. In case of the extended CP, the number of OFDM symbols allocated to one slot may be 6. When a channel state is unstable, such as a case in which a UE moves at a high speed, the extended CP can be used to reduce inter-symbol interference.

When the normal CP is used, one subframe includes 14 OFDM symbols since one slot has 7 OFDM symbols. The first three OFDM symbols at most in each subframe can be allocated to a PDCCH and the remaining OFDM symbols can be allocated to a PDSCH.

FIG. 2( b) illustrates a type-2 radio frame structure. The type-2 radio frame includes 2 half frames. Each half frame includes 5 subframes, a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS), and one subframe consists of 2 slots. The DwPTS is used for initial cell search, synchronization or channel estimation. The UpPTS is used for channel estimation in a BS and UL transmission synchronization acquisition in a UE. The GP eliminates UL interference caused by multi-path delay of a DL signal between a UL and a DL.

The radio frame structure is merely exemplary and the number of subframes included in the radio frame, the number of slots included in a subframe, and the number of symbols included in a slot can be vary.

FIG. 3 illustrates a resource grid of a downlink slot.

Referring to FIG. 3, a downlink slot includes a plurality of OFDM symbols in the time domain. One downlink slot may include 7(6) OFDM symbols, and one resource block (RB) may include 12 subcarriers in the frequency domain. Each element on the resource grid is referred to as a resource element (RE). One RB includes 12×7(6) REs. The number N_(RB) of RBs included in the downlink slot depends on a downlink transmit bandwidth. The structure of an uplink slot may be same as that of the downlink slot except that OFDM symbols by replaced by SC-FDMA symbols.

FIG. 4 illustrates an uplink subframe structure.

Referring to FIG. 4, an uplink subframe includes a plurality of (e.g. 2) slots. A slot may include different numbers of SC-FDMA symbols according to CP lengths. For example, a slot can include 7 SC-FDMA symbols in the case of normal CP. The uplink subframe is divided into a control region and a data region. The data region includes a PUSCH and is used to carry a data signal such as audio data. The control region includes a PUCCH and is used to carry UCI. The PUCCH includes an RB pair (e.g. m=0, 1, 2, 3) located at both ends of the data region in the frequency domain and hopped in a slot boundary.

FIG. 5 illustrates PUCCH formats 2/2a/2b in case of normal CP and FIG. 6 illustrates PUCCH formats 2/2a/2b in case of extended CP. Referring to FIGS. 5 and 6, one subframe includes 10 QPSK data symbols in addition to RS symbols in case of normal CP. Each of the QPSK symbols is spread in the frequency domain according to CS and then mapped to a corresponding SC-FDMA symbol. SC-FDMA symbol level CS hopping may be applied to randomize inter-cell interference. An RS may be multiplexed according to CDM using CSs. For example, if the number of available CSs is 12 or 6, 12 or 6 UEs can be multiplexed in the same physical resource block (PRB).

CSI (e.g. CQI, PMI and RI) and a combination of CSI and ACK/NACK may be transmitted through PUCCH formats 2/2a/2b. In this case, Reed-Muller (RM) channel coding is applicable.

Channel coding for a UI CSI in LTE is described as follows. A bit stream a₀, a₁, a₂, a₃, . . . , a_(A-1) is channel-coded using RM code (20,A). Table 1 shows a base sequence for code (20,A). Here, a₀ and a_(A-1) denote a most significant bit (MSB) and a least significant bit (LSB). In the case of extended CP, a maximum number of information bits is 11 in cases other than a case in which CSI and ACK/NACK are simultaneously transmitted. The CQI may be subjected to QPSK after being coded into 20 bits using the RM code. The coded bits may be scrambled before being subjected to QPSK.

TABLE 1 I M_(i,0) M_(i,1) M_(i,2) M_(i,3) M_(i,4) M_(i,5) M_(i,6) M_(i,7) M_(i,8) M_(i,9) M_(i,10) M_(i,11) M_(i,12) 0 1 1 0 0 0 0 0 0 0 0 1 1 0 1 1 1 1 0 0 0 0 0 0 1 1 1 0 2 1 0 0 1 0 0 1 0 1 1 1 1 1 3 1 0 1 1 0 0 0 0 1 0 1 1 1 4 1 1 1 1 0 0 0 1 0 0 1 1 1 5 1 1 0 0 1 0 1 1 1 0 1 1 1 6 1 0 1 0 1 0 1 0 1 1 1 1 1 7 1 0 0 1 1 0 0 1 1 0 1 1 1 8 1 1 0 1 1 0 0 1 0 1 1 1 1 9 1 0 1 1 1 0 1 0 0 1 1 1 1 10 1 0 1 0 0 1 1 1 0 1 1 1 1 11 1 1 1 0 0 1 1 0 1 0 1 1 1 12 1 0 0 1 0 1 0 1 1 1 1 1 1 13 1 1 0 1 0 1 0 1 0 1 1 1 1 14 1 0 0 0 1 1 0 1 0 0 1 0 1 15 1 1 0 0 1 1 1 1 0 1 1 0 1 16 1 1 1 0 1 1 1 0 0 1 0 1 1 17 1 0 0 1 1 1 0 0 1 0 0 1 1 18 1 1 0 1 1 1 1 1 0 0 0 0 0 19 1 0 0 0 0 1 1 0 0 0 0 0 0

Channel-coded bits b₀, b₁, b₂, b₃, . . . , b_(B-1) may be generated according to Equation 1.

$\begin{matrix} {{b_{i} = {\sum\limits_{n = 0}^{A - 1}\;{\left( {a_{n} \cdot M_{i,n}} \right){mod}\mspace{14mu} 2}}}{Here},{i = 0},1,2,\ldots\mspace{14mu},{B - 1.}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack \end{matrix}$

Table 2 shows an uplink control information (UCI) field for wideband report (single antenna port, transmit diversity or open loop spatial multiplexing PDSCH) CSI feedback.

TABLE 2 Field Bits Wideband CQI 4

Table 3 shows a UCI field for wideband CQI and PMI feedback.

TABLE 3 Bits 2 antenna ports 4 antenna ports Field Rank = 1 Rank = 2 Rank = 1 Rank > 1 Wideband CQI 4 4 4 4 Spatial differential 0 3 0 3 CQI PMI (Precoding 2 1 4 4 Matrix Index)

Table 4 shows a UCI field for RI feedback for wideband report.

TABLE 4 Bits 4 antenna ports Field 2 antenna ports Maximum 2 layers Maximum 4 layers RI (Rank 1 1 2 Indication)

FIG. 7 illustrates a signal processing procedure through which a UE transmits an uplink signal.

Referring to FIG. 7, a scrambling module 201 may scramble a transmitted signal using a UE-specific scramble signal. The scrambled signal is input to a modulation mapper 202 in which the scrambled signal is modulated into complex symbols using Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) or 16-Quadrature amplitude Modulation (QAM)/64-QAM according to signal type and/or channel status. The modulated complex symbols are processed by a transform precoder 203, and then applied to a resource element mapper 204. The resource element mapper 204 may map the complex symbols to resource elements. The signal processed in this manner may be subjected to an SC-FDMA signal generator 205 and transmitted to a BS through an antenna.

FIG. 8 illustrates SC-FDMA and OFDMA schemes. 3GPP employs OFDMA in downlink and uses SC-FDMA in uplink.

Referring to FIG. 8, both a UE for transmitting an uplink signal and a BS for transmitting a downlink signal include a serial-to-parallel converter 401, a subcarrier mapper 403, an M-point IDFT module 404, and a cyclic prefix (CP) adder 406. The UE for transmitting a signal according to SC-FDMA additionally includes an N-point DFT module 402. The N-point DFT module 402 offsets the influence of IDFT processing of the M-point IDFT module 404 such that a transmitted signal has single carrier property.

FIG. 9 illustrates a signal processing procedure for mapping DFT process output samples to a single carrier in clustered SC-FDMA. FIGS. 10 and 11 illustrate a signal processing procedure for mapping DFT process output samples to multiple carriers in clustered SC-FDMA. FIG. 9 shows an example of application of intra-carrier clustered SC-FDMA while FIGS. 10 and 11 show examples of application of inter-carrier clustered SC-FDMA. FIG. 10 illustrates a case in which a signal is generated through a single IFFT block when subcarrier spacing between neighboring component carriers is set while component carriers are contiguously allocated in the frequency domain. FIG. 11 shows a case in which a signal is generated through a plurality of IFFT blocks when component carriers are non-contiguously allocated in the frequency domain.

FIG. 12 illustrates a signal processing procedure in segmented SC-FDMA.

Segmented SC-FDMA is a simple extension of the DFT spreading and IFFT subcarrier mapping structure of the conventional SC-FDMA, when the number of DFT blocks is equal to the number of IFFT blocks and thus the DFT blocks and the IFFT blocks are in one-to-one correspondence. While the term ‘segmented SC-FDMA’ is adopted herein, it may also be called N×SC-FDMA or N×DFT spread OFDMA (N×DFT-s-OFDMA). Referring to FIG. 12, the segmented SC-FDMA is characterized in that total time-domain modulated symbols are divided and assigned to N groups (N is an integer larger than 1) and a DFT process is performed on a group-by-group basis to relieve the single carrier property constraint.

A multi-carrier system or a carrier aggregation system means a system using aggregation of a plurality of carriers (in other words, component carriers) having a bandwidth narrower than a target bandwidth for supporting a wideband. When the plurality of carriers having a bandwidth narrower than the target bandwidth are aggregated, the bandwidth of the aggregated carriers may be limited to the bandwidths used in existing systems for backward compatibility with the existing systems. For example, an LTE system supports bandwidths of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz and an LTE-A system evolved from the LTE system can support bandwidths wider than 20 MHz using bandwidths supported by the LTE system. Alternatively, a new bandwidth may be defined to support carrier aggregation irrespective of the bandwidths used in existing systems. The term ‘multi-carrier’ can be used with carrier aggregation and bandwidth aggregation. Carrier aggregation includes both contiguous carrier aggregation and non-contiguous carrier aggregation.

FIG. 13 illustrates a concept of management of downlink component carriers in a BS and FIG. 14 illustrates a concept of management of uplink component carriers in a UE. For convenience, a higher layer is a MAC layer in the following description. The term ‘component carrier’ can be replaced by an equivalent term (e.g. cell).

FIG. 15 illustrates a concept of management of multiple carriers by one MAC layer in a BS and FIG. 16 illustrates a concept of management of multiple carriers by one MAC layer in a UE.

Referring to FIGS. 15 and 16, one MAC layer manages and operates one or more frequency carriers for transmission and reception. In this case, resource management is flexible because frequency carriers managed by one MAC layer need not be contiguous. In FIGS. 15 and 16, one PHY layer corresponds to one component carrier. Here, one PHY layer does not necessarily mean an independent radio frequency (RF) device. While one independent RF device means one PHY layer in general, one RF device is not limited thereto and may include multiple PHY layers.

FIG. 17 illustrates a concept of management of multiple carriers by multiple MAC layers in a BS and FIG. 18 illustrates a concept of management of multiple carriers by multiple MAC layers in a UE. FIG. 17 illustrates another concept of management of multiple carriers by multiple MAC layers in a BS and FIG. 18 illustrates another concept of management of multiple carriers by multiple MAC layers in a UE.

Distinguished from the structures shown in FIGS. 15 and 16, multiple carriers may be controlled by multiple MAC layers instead of one MAC layer as shown in FIGS. 17 to 20.

Multiple MAC layers may control one-to-one multiple carriers as shown in FIGS. 17 and 18. Referring to FIGS. 19 and 20, MAC layers may control one-to-one some carriers and one MAC layer may control other carriers.

The above-described system includes one to N carriers which are contiguous or non-contiguous. A TDD system is constructed such that N carriers for downlink transmission and uplink transmission are operated and an FDD system is constructed such that multiple carriers are respectively used for uplink and downlink. The FDD system may support asymmetrical carrier aggregation in which the number of aggregated carriers and/or a carrier bandwidth in uplink is different from those in downlink.

In the case of DL non-cross-carrier scheduling, a PDCCH and a corresponding PDSCH are transmitted in the same DL CC. For example, if the PDCCH is transmitted in DL CC #0, the corresponding PDSCH is also transmitted in the DL CC #0. In the case of cross-carrier scheduling, the PDCCH and PDSCH are transmitted in different DL CCs. In the case of UL cross-carrier scheduling, a PDCCH and a corresponding PUSCH are transmitted using a linked DL CC-UL CC pair according to a system information block (SIB). For example, when DL CC #1 and UL CC #1 are paired according to SIB2, if the PDCCH is transmitted in DL CC #1, the corresponding PUSCH is transmitted in UL CC #1. In the case of cross-carrier scheduling, the PDCCH and the corresponding PUSCH are transmitted in different DL CC-UL CC pairs. For example, when DDL CC #0 and UL CC #0 are paired and DL CC #1 and UL CC #1 are paired according to SIB2, the PDCCH may be transmitted in DL CC #1 and the corresponding PUSCH may be transmitted in UL CC #0. A DL CC and A UL CC scheduled by the PDCCH in cross-carrier scheduling are indicated through a carrier indicator field (CIF) in a DCI format.

DL/UL CCs include DL/UL primary CCs and DL/UL secondary CCs. The DL primary CC may be defined as a DL CC linked with the UL primary CC. Here, linkage includes both implicit linkage and explicit linkage. In LTE, a DL CC and a UL CC are uniquely paired. For example, a DL CC linked with the UL primary CC according to LTE pairing may be called a DL primary CC. This can be regarded as implicit linkage. Explicit linkage refers to previous configuration of linkage by a network and may be signaled through a radio resource control (RRC) message. In explicit linkage, a DL CC linked with the UL primary CC may be called a DL primary CC. Here, the UL primary CC may be a UL CC carrying a PUCCH. The DL primary CC may be configured through higher layer signaling. The DL primary CC may be a DL CC through which a UE performs initial access. DL CCs other than the DL primary CC may be called DL secondary CCs. Similarly, UL CCs other than the UL primary CC may be called UL secondary CCs.

In LTE-A, the concept of a cell is used to manage radio resources. A cell is defined as a combination of downlink resources and uplink resources. Yet, the uplink resources are not mandatory. Therefore, a cell may be composed of downlink resources only or both downlink resources and uplink resources. The linkage between the carrier frequencies (or DL CCs) of downlink resources and the carrier frequencies (or UL CCs) of uplink resources may be indicated by system information. A cell operating in primary frequency resources (or a PCC) may be referred to as a primary cell (PCell) and a cell operating in secondary frequency resources (or an SCC) may be referred to as a secondary cell (SCell). Simply, a DL CC and a UL CC may be respectively called a DL cell and a UL cell. Furthermore, a DL primary CC and a UL primary CC may be respectively called a DL PCell and a UL PCell. The PCell is used for a UE to establish an initial connection or re-establish a connection. The PCell may refer to a cell indicated during handover. The SCell may be configured after an RRC connection is established and may be used to provide additional radio resources. The PCell and the SCell may collectively be referred to as a serving cell. Accordingly, a single serving cell composed of a PCell only exists for a UE in an RRC_Connected state, for which CA is not set or which does not support CA. On the other hand, a plurality of serving cells including a PCell and one or more SCells can be configured for a UE in an RRC_CONNECTED state, for which CA is set. A network may configure one or more SCells in addition to an initially configured PCell, for a UE supporting CA during connection setup after an initial security activation operation is initiated.

DL-UL pairing may correspond to FDD only. DL-UL pairing may not be additionally defined for TDD because TDD uses the same frequency. DL-UL linkage may be determined from UL linkage through UL E-UTRA absolute radio frequency channel number (EARFCN) information of SIB2. For example, DL-UL linkage can be obtained through SIB2 decoding in the event of initial access and acquired through RRC signaling in other cases. Accordingly, only SIB2 linkage is present and other DL-UL pairings may not be explicitly defined. For example, in a 5DL:1UL structure, DL CC#0 and UL CC#0 have an SIB2 linkage relationship and other DL CCs may have the SIB2 linkage relationship with other UL CCs that are not set to the corresponding UE.

FIG. 21 illustrates channel status information generation and transmission.

Referring to FIG. 21, a UE measures downlink quality using a reference signal and reports channel status information to a BS. The BS performs downlink scheduling (UE selection, resource allocation, etc.) according to the reported channel status information. The channel status information includes at least one of CQI, PMI and RI. The CQI may be generated through various methods. For example, channel state (or spectral efficiency) can be quantized and signaled, an SINR can be calculated and signaled or a channel application state such as a modulation and coding scheme (MCS) can be signaled in order to generate the CQI.

In LTE, a common RS (CRS) is used for channel measurement. The CRS is used for channel information acquisition and data demodulation and transmitted per subframe. In LTE-A, a channel state information RS (CSI-RS) for channel measurement only may be used. The CSI-RS is intermittently transmitted on the time domain in order to reduce overhead. For example, the CSI-RS can be periodically transmitted at an interval of an integer multiple of a subframe or transmitted in a specific pattern. The period or pattern in which the CSI-RS is transmitted may be set by a BS.

FIG. 22 illustrates a CSI (e.g. CQI, PMI and RI) reporting scheme. Referring to FIG. 22, CSI reporting is divided into periodic reporting and aperiodic reporting.

Periodic CSI reporting refers to reporting channel quality by a UE at a predetermined time without additional signaling. Since CSI configuration information (e.g. CSI reporting period and a subframe offset for CSI reporting) for CSI reporting in a single carrier situation is set per CSI (e.g. CQI, PMI and RI), transmissions of different pieces of CSI information may collide in the same subframe. In this case, to handle collision, transmission of specific CSI can be dropped in a subframe in which CSI collision occurs based on CSI importance (e.g. RI>CQI, wideband CSI>subband CSI) or transmission of CSI having a short CSI reporting period can be dropped.

Aperiodic CSI reporting refers to a process through which a network requests a UE to report CSI through explicit signaling as necessary. When aperiodic CSI reporting is needed, the network signals an uplink scheduling grant to the UE using DCI format 0. The UE performs aperiodic CSI reporting when a CSI request value of DCI format 0 is 1. Aperiodic CSI reporting (i.e. CSI request=1) is divided into a CSI only (transmission) mode and a CSI+data (transmission) mode. When the CSI request value is 1, an MCS index I_(MCS) is 29 and the number of allocated PRBs is less than 4 (N_(PRB)≦4), the UE interprets the corresponding signaling as the CSI only mode. In other cases, the UE interprets the corresponding signaling as the CSI+data mode. In the CSI only mode, the UE transmits only CSI without data (i.e. UL-SCH (Uplink Shared Channel) transport block) on a PUSCH. In the CSI+data mode, the UE transmits CSI and data on a PUSCH. The CSI only mode may be normalized and called a feedback only mode and the CSI+data mode may be called a feedback+data mode.

Table 5 shows part of DCI format 0 indicating aperiodic PUSCH feedback in LTE. When a CQI request field is set to 1, the number of physical resource blocks (PRBs) is less than 4 and MCS index I_(MCS) is set to 29 in DCI format 0, the UE feeds back downlink channel information (or channel state information (CSI)) on a PUSCH.

TABLE 5 bits aperiodic PUSCH Feedback RB assignment 7 PRB <= 4 MCS 5 I_(MCS) = 29 CQI request 1 1 *MCS: modulation and coding scheme

FIG. 23 illustrates a procedure of processing UL-SCH data and control information. When a UE attempts to transmit control information in a subframe to which PUSCH transmission is assigned, the UE multiplexes control information (UCI) and UL-SCH data before DFT-spreading. While periodic CSI is transmitted on a PUCCH, the periodic CSI is piggyback on the PUSCH when transmitted in a subframe to which PUSCH transmission is allocated. Aperiodic CSI is transmitted in PUSCH format 2/2a/2b.

Referring to FIG. 23, error detection is performed by attaching a CRC (Cyclic Redundancy Check) to a UL-SCH transport block (S100).

The whole UL-SCH transport block is used to calculate a CRC parity bit. The transport block is composed of bits a₀, a₁, a₂, a₃, . . . , a_(A-1). Parity bits are p₀, p₁, p₂, p₃, . . . , p_(L-1). The transport block has a size of A and the number of parity bits is L.

After attachment of the CRC to the transport block, code block segmentation and code block CRC attachment are performed (S110). Bits b₀, b₁, b₂, b₃, . . . , b_(B-1) are input for code block segmentation. B represents the number of bits of the transport block (including the CRC). After code block segmentation, bits c_(r0), c_(r1), c_(r2), c_(r3), . . . , c_(r(K) _(r) ₋₁₎ are acquired. Here, r denotes a code block number (r=0, 1, . . . , C−1) and Kr denotes the number of bits of a code block r. C represents the number of code blocks.

Channel coding follows code block segmentation and code block CRC attachment (S120). Bits d_(r0) ^((i)), d_(r1) ^((i)), d_(r2) ^((i)), d_(r3) ^((i)), . . . , d_(r(D) _(r) ₋₁₎ ^((i)) are generated from channel coding. Here, i=0, 1 and 2, D_(r) denotes the number of bits of an i-th coded stream for the code block r (i.e. D_(r)=K_(r)+4), r denotes a code block number (r=0, 1, . . . , C−1) and Kr denotes the number of bits of the code block r. C represents the number of code blocks. Turbo coding may be used for channel coding.

Rate matching is performed after channel coding (S130). Bits e_(r0), e_(r1), e_(r2), e_(r3), . . . , e_(r(E) _(r) ₋₁₎ are generated from rate matching. Here, E_(r) denotes the number of rate-matched bits of an r-th code block (r=0, 1, . . . , C−1) and C denotes the number of code blocks.

Code block connection is performed after rate matching (S140). Bits f₀, f₁, f₂, f₃, . . . , f_(G-1) are generated from code block connection. Here, G denotes the number of encoded bits for transmission. When the control information is multiplexed with UL-SCH transmission, bits used for control information transmission are not included in G. Bits f₀, f₁, f₂, f₃, . . . , f_(G-1) correspond to a UL-SCH codeword.

In case of uplink control information, channel quality information (CQI and/or PMI), RI and HARQ-ACK are independently channel-coded. Channel coding of UCI is performed based on the number of encoded symbols for control information. For example, the number of encoded symbols can be used for rate matching of encoded control information. The number of encoded symbols corresponds to the number of modulation symbols and the number of REs in the following processes.

Channel coding of channel quality information is performed using an input bit sequence o₀, o₁, o₂, . . . , o_(O-1) (S150). An output bit sequence q₀, q₁, q₂, q₃, . . . , q_(Q) _(CQI) ₋₁ is obtained from channel coding of the channel quality information. A channel coding scheme applied to channel coding of the channel quality information depends on the number of bits of the channel quality information. When the channel quality information is 11 bits or more, a CRC bit is added thereto. Q_(CQI) denotes the number of encoded bits. The encoded channel quality information may be rate-matched in order to adjust the length of the bit sequence to Q_(CQI). Q_(CQI)=Q′_(CQI)×Q_(m), Q′_(CQI) denotes the number of encoded symbols for CQI and Q_(m) represents a modulation order. Q_(m) is set to be equal to that of the UL-SCH data.

Channel coding of RI is performed using an input bit sequence [o₀ ^(RI)] or [o₀ ^(RI)o₁ ^(RI)] (S160). [o₀ ^(RI)] and [o₀ ^(RI)o₁ ^(RI)] respectively represent 1-bit RI and 2-bit RI.

In the case of 1-bit RI, repetition coding is used. For the 2-bit RI, a (3,2) simplex code is used and encoded data can be cyclically repeated. An output bit sequence q₀ ^(RI), q₁ ^(RI), q₂ ^(RI), . . . , q_(Q) _(RI) ₋₁ ^(RI) is acquired according to combination of encoded RI blocks. Here, Q_(RI) denotes the number of encoded bits. To adjust the length of the encoded RI to Q_(RI), part of the encoded RI blocks may be lastly combined (i.e. rate matching). Q_(RI)=Q′_(RI)×Q_(m), Q′_(RI) denotes the number of encoded symbols for RI and Q_(m) represents a modulation order. Q_(m) is set to be equal to that of the UL-SCH data.

Channel coding of HARQ-ACK is performed using an input bit sequence [o₀ ^(ACK)] [o₀ ^(ACK)o₁ ^(ACK)] or [o_(o) ^(ACK)o₁ ^(ACK)o_(o) _(ACK) ₋₁ ^(ACK)] (S170). [o₀ ^(ACK)] and [o₀ ^(ACK)o₁ ^(ACK)] respectively represent 1-bit HARQ-ACK and 2-bit HARQ-ACK and [o₀ ^(ACK)o₁ ^(ACK)o_(o) _(ACK-1) ^(ACK)] represents HARQ-ACK composed of information of two bits or more (i.e. o^(ACK)>2). ACK is encoded into 1 and NACK is encoded into 0. For the 1-bit HARQ-ACK, repetition coding is used. In case of the 2-bit HARQ ACK, (3,2) simplex code is used and encoded data may be cyclically repeated. Q_(ACK) denotes the number of encoded bits. A bit sequence q₀ ^(ACK), q₁ ^(ACK), q₂ ^(ACK), . . . , q_(Q) _(ACK) ₋₁ ^(ACK) is obtained according to combination of encoded HARQ-ACK blocks. To adjust the length of the bit sequence to Q_(ACK), part of the encoded HARQ-ACK blocks may be finally combined (i.e. rate matching). Q_(ACK)=Q′_(ACK)×Q_(m), Q′_(ACK) denotes the number of encoded symbols for HARQ-ACK and Q_(m) represents a modulation order. Q_(m) is set to be equal to that of the UL-SCH data.

The encoded UL-SCH bits f₀, f₁, f₂, f₃, . . . , f_(G-1) and the encoded CQI/PMI bits q₀, q₁, q₂, q₃, . . . , q_(Q) _(CQI) ₋₁ are input to a data/control multiplexing block (S180). The data/control multiplexing block outputs g₀, g₁, g₂, g₃, . . . , g_(H′-1). Here, g_(i) denotes a column vector of Q_(m) (i=0, H′−1) and H=(G+Q_(CQI)). H represents the number of encoded bits allocated for the UL-SCH data and CQI/PMI.

The output g₀, g₁, g₂, g₃, . . . , g_(H′-1) of the data/control multiplexing block, the encoded RI q₀ ^(RI), q₁ ^(RI), q₂ ^(RI), . . . , q_(Q) _(RI) ₋₁ ^(RI) and the encoded HARQ-ACK q₀ ^(ACK), g₁ ^(ACK), q₂ ^(ACK), . . . , q_(Q) _(ACK) ₋₁ ^(ACK) are input to a channel interleaver (S190). Here, g_(i) denotes a column vector of Q_(m) (i=0, H′−1) for CQI/PMI (H′=H/Q_(m)), q_(i) ^(ACK) is a column vector of Q_(m)(i=0, Q′_(ACK)−1) for ACK/NACK (Q′_(ACK)=Q_(ACK)/Q_(m)) and q_(i) ^(RI) is a column vector of Q_(m) (i=0, Q′_(RI)−1) for RI (Q′_(RI)=Q_(RI)/Q_(m)).

The channel interleaver multiplexes the control information for PUSCH transmission and the UL-SCH data. Specifically, the channel interleaver maps the control information and UL-SCH data to a channel interleaver matrix corresponding to a PUSCH resource.

After channel interleaving, a bit sequence h₀, h₁, h₂, . . . , h_(H+Q) _(RI) ₋₁ read from the channel interleaver matrix column by column is output from the channel interleaver. The read bit sequence is mapped to a resource grid. H″=H′+Q′_(RI) modulation symbols are transmitted through subframes.

FIG. 24 illustrates multiplexing of control information and UL-SCH data on a PUSCH. The control information includes at least one of CQI/PMI, HARQ ACK/NACK and RI. The number of REs used to transmit each of CQI/PMI, ACK/NACK and RI is based on a modulation and coding scheme (MCS) and an offset value (Δ_(offset) ^(CQI), Δ_(offset) ^(HARQ-ACK), Δ_(offset) ^(RI)) allocated for PUSCH transmission. The offset value permits different coding rates according to control information and is semi-statically set through higher layer (RRC) signaling. The UL-SCH data and the control information are not mapped to the same RE. The control information is mapped to two slots of a subframe. The BS can easily demultiplex the control information and a data packet because the BS can be previously aware of transmission of the control information on a PUSCH.

Referring to FIG. 24, CQI and/or PMI (CQI/PMI) are disposed at the start of a UL-SCH data resource, sequentially mapped to all SC-FDMA symbols on a subcarrier and then mapped in the next subcarrier. The CQI/PMI is mapped in a subframe from the left to the right, that is, in a direction in which an SC-FDMA symbol index increases. The UL-SCH data is rate-matched in consideration of the quantity of CQI/PMI (i.e. the number of encoded symbols) and mapped in the same manner as CQI/PMI mapping after the CQI/PMI is mapped. When the CQI/PMI size (payload size) is small (e.g. less than 11 bits), a block code (32, k) is used for the CQI/PMI similarly to PUCCH transmission and encoded data can be cyclically repeated. When the CQI/PMI size is small, a CRC is not used. If the CQI/PMI size is large (e.g. greater than 11 bits), an 8-bit CRC is added to the CQI/PMI and channel coding and rate matching are performed on the CQI/PMI using a tail-biting convolutional code. ACK/NACK is inserted into part of SC-FDMA resources to which the UL-SCH data is mapped through puncturing. The ACK/NACK is disposed by an RS and mapped to corresponding SC-FDMA symbols starting from the lowest SC-FDMA symbol, that is, in a direction in which a subcarrier index increases. In case of normal CP, SC-FDMA symbols for the ACK/NACK correspond to SC-FDMA symbols #2/#5 in each slot, as shown in FIG. 24. Encoded RI is disposed by the symbols corresponding to the ACK/NACK irrespective of whether the ACK/NACK is actually transmitted in the corresponding subframe. The ACK/NACK, RI and CQI/PMI are independently encoded.

In LTE, control information (e.g. using QPSK) can be scheduled to be transmitted on a PUSCH without UL-SCH data. Specifically, in case of the CQI only mode of FIG. 22, a UE transmits channel state information only without a UL-SCH transport block. In this case, control information (CQI/PMI, RI and/or ACK/NACK) is multiplexed prior to DFT-spreading in order to maintain a single-carrier characteristic of low CM (cubic metric). Multiplexing of the ACK/NACK, RI and CQI/PMI is performed through a process similar to that shown in FIG. 23.

FIG. 25 illustrates a heterogeneous network (HetNet) including a macro cell and a micro cell. Next-generation communication standards including LTE-A discuss a heterogeneous network in which a micro cell having a low transmit power is present within a conventional macro-cell coverage.

Referring to FIG. 25, the macro cell may overlap one or more micro cells. A macro cell service is provided by a macro eNB (MeNB). In the specification, the term ‘macro cell’ and the term ‘macro eNB’ can be used interchangeably. A UE linked to the macro cell may be called a macro UE. The macro UE receives a downlink signal from the MeNB and transmits an uplink signal to the MeNB.

A micro cell is also called a femto cell or a pico cell. Micro cell service is provided by a pico eNB, home eNB (HeNB), relay node (RN), etc. The pico eNB, HeNB and RN are commonly called an HeNB for convenience. Here, the term ‘micro cell’ and ‘home eNB’ may be interchangeably used. A UE linked with a micro cell may be called a micro UE or a home UE. The home UE receives a downlink signal from the HeNB and transmits an uplink signal to the HeNB.

Microcells may be categorized into an open access (OA) cell and a closed subscriber group (CSG) cell according to accessibility. The OA cell refers to a micro cell in which a UE can be provided with a service as necessary without access restriction. The CSG cell refers to a micro cell in which only a specific permitted UE can be provided with a service.

Since the macro cell and micro cell overlap each other in the heterogeneous network, inter-cell interference is problematic. When a macro UE is located at the boundary of the macro cell and the micro cell, as shown in FIG. 25, a downlink signal from an HeNB may be applied as interference to a home UE in the micro cell. Furthermore, an uplink signal from the macro UE may act as interference on the HeNB. Similarly, an uplink signal from the home UE may act as interference on the macro eNB.

As described above, in a macro-pico heterogeneous network, a macro cell may apply severe interference to a pico UE, particularly, a pico UE located at a cell boundary. Accordingly, a method for cancelling uplink/downlink interference applied to data, an L1/L2 control signal, a synchronization signal and a reference signal is needed. Inter-cell interference cancellation (ICIC) may be handled in the time, frequency and/or spatial domains.

FIG. 26 illustrates a method for cancelling inter-cell interference in a HetNet. Assuming that a target that needs to be protected from inter-cell interference is a pico UE for convenience an aggressor causing interference is a macro cell (or macro eNB). This example relates to a case in which an aggressor cell uses a time domain interference cancellation method.

Referring to FIG. 26, the macro cell causing inter-cell interference can allocate an almost blank subframe (ABS) (or ABSF) to a radio frame. The ABS refers to a subframe SubF in which DL signals other than a specific DL signal are not transmitted (or DL signal transmission/power is limited or DL interference is restricted). The ABS can be repeated such that it has a specific pattern in one or more radio frames (e.g. 4 radio frames). In the example of FIG. 26, the ABS is set to subframes #2/#6.

The macro cell signals an ABS configuration (e.g. 40-bit bitmap) to the pico cell through a backhaul link and the pico cell can schedule a pico UE using the ABS configuration. For example, a (cell boundary) pico UE can be scheduled in an ABS period only. That is, the pico UE can receive a less interfering signal from the pico cell by being scheduled in the same pico subframe as the ABS. Accordingly, a UE (i.e. pico UE) of a victim cell, particularly, the cell edge UE needs to report CSI about a less interfered subframe for efficient scheduling. However, when interfered subframes are inevitably allocated to edge UEs because of a large number of edge UEs or for efficient scheduling, the corresponding UEs need to be able to report CSI about interfered subframes.

A set of less interfered subframes and a set of interfered subframes are referred to as restricted subsets. When a plurality of restricted subsets is configured, one of the restricted subsets may be configured such that it corresponds to an ABS pattern of an aggressor cell. However, the restricted subset does not necessarily correspond to the ABS pattern. Furthermore, the restricted subsets may be configured such that they have no common subframe or have a predetermined number of common subframes. The sum of subframes included in the two restricted subsets may correspond to the total number of subframes or the subframes included in the two restricted subsets may be a subset of all subframes. That is, the restricted subsets refer to subframe sets in which channel measurement for CSI reporting is permitted. Two restricted subsets are defined through RRC signaling in a conventional system.

FIG. 27 illustrates configuration of restricted subsets and aperiodic CSI reporting in a single carrier situation. In FIG. 27, each block represents a subframe.

Referring to FIG. 27, plural restricted subsets (e.g. restricted subset #1 and restricted subset #2) for one or more radio frames are independently configured. Each restricted subset may be configured through higher layer (e.g. RRC) signaling and a detailed pattern thereof may be indicated using a bitmap. For example, bit positions in the bitmap respectively correspond to subframes in a restricted subset configuration period. When a bit value is 1, channel measurement in the corresponding subframe is permitted. When a bit value is 0, channel measurement may be prohibited in the corresponding subframe. A restricted subset pattern cycle may correspond to an ABS pattern cycle (e.g. 40 ms, 4 radio frames). One of restricted subsets #1 and #2 may correspond to an ABS pattern but may be operated such that it does not correspond to the ABS pattern. Similarly, the other may be operated such that it does not correspond to a non-ABS pattern although it may correspond to the non-ABS pattern. In FIG. 27, a UE independently performs periodic/aperiodic CSI reporting for each restricted subset.

In the case of periodic CSI reporting, a scheme similar to CA configured of 2 CCs is applied and CSI on the restricted subsets are separately reported. Since CSI reports on the restricted subsets are transmitted at independent intervals, CSI transmissions may collide with each other at the same instant. To solve this problem, an eNB can previously signal an offset value applied to the restricted subsets during CSI reporting to the UE through RRC signaling.

In the case of aperiodic CSI reporting, the eNB triggers a CSI report on a desired restricted subset in consideration of positions of subframes in which available CSI resources (e.g. CRS, CSI-RS or the like) are present and triggering time (e.g. a subframe in which a PDCCH signal indicating CSI report is received). For example, when a triggering message (e.g. PDCCH signal indicating CSI report) is received in a subframe belonging to restricted subset #1, the UE performs CSI reporting on restricted subset #1. However, CSI reporting operation of the UE may be changed in the following situations.

-   -   1. Case in which a CSI resource is present in a DL subframe         including a triggering message     -   2. Case in which a CSI resource is not present in a DL subframe         including a triggering message

In the former case, the UE can measure channel state in a subframe (referred to as a triggering subframe hereinafter) including the triggering message and then perform CSI reporting in a subframe corresponding to the triggering subframe+k (e.g. k=4). In the latter case, the UE can determine a restricted subset to which the subframe including the triggering subframe belongs and then perform channel state measurement and CSI reporting using the nearest subframe including the CSI resource from among subframes included in the restricted subset of the same type.

As described above, a single-carrier system need not transmit additional information for indicating a specific restricted subset because the single-carrier system implicitly indicates a restricted subset corresponding to a CSI reporting target according to the position of the triggering subframe when aperiodic CSI reporting is performed. However, the CSI resource may be a CRS or CSI-RS according to transmission mode, and thus the position of the triggering subframe may be limited for efficient CSI reporting in the case of aperiodic CSI reporting using the CSI-RS.

A CA system uses a method of explicitly indicating a restricted subset corresponding to a CSI reporting target when aperiodic CSI reporting is performed. For example, it is possible to previously configure a CSI report set through RRC and then designate a CSI reporting target through a CSI request field of a PDCCH. Table 7 shows a CSI request field and a CSI reporting target.

TABLE 7 Value of CSI request field (bits) Description 00 No aperiodic CSI report is triggered. 01 Aperiodic CSI report triggered for serving cell c 10 Aperiodic CSI report is triggered for a 1^(st) set of serving cells configured by higher layers. 11 Aperiodic CSI report is triggered for a 2^(nd) set of serving cells configured by higher layers.

Referring to Table 7, when the CSI request field indicates 10 or 11, the UE needs to transmit CSI on the first or second set of serving cells. Since aperiodic CSI report triggering is performed on a CC set basis, CSI request bits are saved. However, CSI reporting is performed on a CC set basis even when only CSI for a specific CC is needed, and thus CSI on other CCs may act as overhead.

FIG. 28 illustrates an example of performing aperiodic CSI reporting in a HetNet supporting CA. It is assumed that a pico UE performs CSI reporting in this example. However, CSI reporting may be performed by a macro UE.

Referring to FIG. 28, plural (e.g. 4) CCs may be configured for a victim cell (e.g. femto cell) and a restricted subset for a edge UE of the femto cell may be configured in one or more CCs. A restricted subset may be independently configured per CC and subframes of the restricted subset may be independently configured per CC. In this case, plural (e.g. 2) subsets for aperiodic CSI reporting may be configured through higher layer (e.g. RRC) signaling. FIG. 28 shows a case in which CC#1 and CC#2 constitute CSI reporting subset #1 and CC#3 and CC#4 constitute CSI reporting subset #2. In CSI reporting subset #1, restricted subsets are configured in CC#1 and CC#2 and a CSI-RS transmission period can be set to 5 subframes (e.g. 5 ms). In CSI reporting subset #2, a restricted subset is not configured in CC#3 and a CSI-RS transmission period can be set to 10 subframes. In CSI reporting subset #2, a restricted subset is configured in CC#4 and a CSI-RS transmission period can be set to 5 subframes. As shown in FIG. 28, the CSI-RS transmission period and a start offset can be independently set per CC.

According to an aperiodic CSI reporting method of a conventional CA system, two CSI reporting subsets are previously configured by a higher layer and a CSI reporting subset corresponding to a CSI reporting target is explicitly indicated during CSI report triggering (refer to Table 7). Accordingly, an eNB transmits a CSI report triggering message (e.g. a PDCCH signal indicating CSI reporting) to a UE and the UE transmits a CSI report on CCs of a CSI report set indicated by a CSI field value in a subframe corresponding to the triggering subframe+k (e.g. k=4). In a CA based HetNet, as shown in FIG. 28, however, conventional CSI reporting set based aperiodic CSI reporting may generate various problems in association with a restricted subset.

A problem of aperiodic CSI reporting with respect to CSI reporting subset #1 is described first. In CSI reporting subset #1, the first triggering time (e.g. triggering subframe) corresponds to restricted subset #1 of CC#1 and restricted subset #2 of CC#2. Accordingly, the UE reports CSI with respect to restricted subset #1 of CC#1 and CSI with respect to restricted subset #2 of CC#2 in a subframe corresponding to the triggering subframe+k (e.g. k=4) in response to the first triggering. The second triggering time (i.e. triggering subframe) corresponds to restricted subframe #2 of CC#1 and restricted subset #1 of CC#2. Accordingly, the UE reports CSI with respect to restricted subset #2 of CC#1 and CSI with respect to restricted subset #1 of CC#2 in a subframe corresponding to the triggering subframe+k (e.g. k=4) in response to the second triggering.

If the second triggering is for acquiring CSI on restricted subset #2 from the point of view of the eNB, the CSI report with respect to restricted subset #1 of CC#2 includes CSI different from CSI intended by the eNB. That is, according to which CC of a CSI reporting subset is used as a basis on which the eNB triggers CSI reporting, a CSI report on another CC in the CSI reporting subset may include CSI about a restricted subset different from that intended by the eNB. This situation frequently occurs as the number of CCs present in a CSI reporting subset increases. In the worst case, the eNB needs to transmit a triggering message twice in order to acquire CSI on a desired restricted subset. This not only generates DL control message overhead but also seriously affects UL throughput because CSI is reported through two PUSCHs.

A problem of aperiodic CSI reporting with respect to CSI reporting subset #2 is described. In the case of CSI reporting subset #2, a problem may be generated when a triggering message is transmitted based on CC#3 in which a restricted subset is not configured. In this case, a CSI report with respect to CC#4 may include CSI on a restricted subset to which a subframe in which CSI is reported belongs and CSI on a subframe in which a CSI-RS is present prior to the subframe in which CSI is reported. Accordingly, the UE can report CSI on a normal subframe for CC#3 and report CSI on restricted subset #1 for CC#4 in response to the first triggering message. The UE can report CSI about restricted subset #1 for CC#4 in response to the second triggering message. In this case, the CSI report with respect to CC#4 may relate to a restricted subset different from a restricted subset that the eNB desires. To solve this problem, the eNB may need to transmit another triggering message to acquire CSI about the desired restricted subset. This generates DL control message overhead and seriously affects UL throughput because CSI is reported through two PUSCHs.

The above-mentioned problem may be aggravated according to a CSI-RS period and a configuration pattern of subframes of a restricted subset. To solve this problem, the present invention proposes various methods for designating a restricted subset for CSI reporting during aperiodic CSI reporting when a plurality of serving cells (or DL CCs) is configured. The present invention is preferably applicable to a CA based HetNet.

FIG. 29 illustrates aperiodic CSI reporting according to an embodiment of the present invention.

Referring to FIG. 29, the eNB can configure one or more CSI reporting subsets through higher layer (e.g. RRC) signaling (S2902). Each CSI reporting subset includes one or more serving cells. It is assumed that CSI reporting subset #1 includes two serving cells (e.g. serving cell #1 and serving cell #2) for convenience. In addition, it is assumed that two restricted subsets (e.g. restricted subset #1 and restricted subset #2) are independently configured for each serving cell. The UE receives a PDCCH signal that requests an aperiodic CSI report on a specific CSI reporting subset in a predetermined subframe (S2904). The PDCCH signal includes a 2-bit CSI request field which indicates CSI triggering and/or a CSI reporting subset that requires a CSI report (refer to Table 7). It is assumed that the CSI request field indicates CSI reporting subset #1 for convenience. In this case, the UE performs CSI reporting on CSI reporting subset #1 (S2906). The CSI report in step S2906 includes CSI on serving cell #1 and CSI on serving cell #2. The CSI report in step S2906 is transmitted to the eNB on a PUSCH (refer to FIGS. 23 and 24).

The CSI on serving cell #1 and CSI on serving cell #2 in step S2906 can be calculated based on a restricted subset given by a predetermined method. When the subframe in which the PDCCH signal is received in step S2904 belongs to different restricted subsets in CSI reporting subset #1, the CSI on serving cell #1 and CSI on serving cell #2 in step S2906 can be calculated based on a restricted subset determined according to a predetermined method. Considering that a restricted subset is a combination of subframes for cell edge UEs of a victim cell, the predetermined scheme may be as follows.

1. A CSI report on a serving cell of a CSI reporting subset may include CSI about the same restricted subset as a reference subset. On the contrary, the CSI report on the serving cell of the CSI reporting subset may include CSI about a restricted subset different from the reference subset. Here, the reference subset refers to a restricted subset to which a subframe of a serving cell (or DL CC) in which a triggering message is transmitted belongs. The serving cell in which the triggering message is transmitted may belong to a CSI reporting subset for which CSI reporting is performed or another CSI reporting subset.

2. Some bits of a UL DCI format in a PDCCH including a triggering message may be used as an indicator for indicating a restricted subset for another serving cell (or DL CC). For example, a spare bit of the UL DCI format can be set to 0 or 1 such that 0 indicates restricted subset #1 and 1 indicates restricted subset #2 or vice versa.

Alternatively, a spare bit of the UL DCI format can be set to 0 or 1 such that 0 indicates reporting of CSI on the same restricted subset as the reference subset and 1 indicates reporting of CSI on a restricted subset including a triggering subframe in a serving cell corresponding to a CSI reporting target, or vice versa.

3. Information about a restricted subset that requires CSI reporting can be transmitted through higher layer (e.g. RRC) signaling. For example, the information about the restricted subset can be transmitted using a bitmap. In this case, a bitmap size can be set to the number of all configured serving cells (or serving cells in which a restricted subset is configured). Here, bit positions in the bitmap may correspond to serving cells, bit value 0 may indicate restricted subset #0 of the corresponding serving cell and bit value 1 may indicate restricted subset #1 of the corresponding serving cell or vice versa. Alternatively, bit value 0 in the bitmap may indicate reporting of CSI on the same restricted subset as the reference subset and bit value 1 may indicate reporting of CSI on a restricted subset including a triggering subframe in the corresponding serving cell, or vice versa.

4. In the case of CSI on a serving cell in which a triggering message is not transmitted, CSI reporting can be performed for a restricted subset different from a restricted subset for which aperiodic CSI reporting has been performed prior to the restricted subset.

5. CSI on a restricted subset including a triggering subframe can be transmitted on a DL CC SIB-linked with a UL CC that reports CSI.

According to aperiodic CSI reporting of a conventional CA system, the eNB needs to transmit a plurality of triggering messages in order to obtain CSI about a desired restricted subset in a CA based HetNet. According to the present invention, however, the eNB need not transmit a plurality of triggering messages to acquire CSI about the desired restricted subset when aperiodic CSI reporting is performed in a CA based HetNet system, and thus UL throughput is not decreased.

FIG. 30 illustrates a BS and a UE applicable to an embodiment of the present invention. When a wireless communication system includes a relay, communication is performed between a BS and the relay on a backhaul link and between the relay and a UE on an access link. Accordingly, the BS or UE shown in FIG. 30 can be replaced by a relay as necessary.

Referring to FIG. 30, an RF communication system includes a BS 110 and a UE 120. The BS 110 includes a processor 112, a memory 114 and an RF unit 116. The processor 112 may be configured to implement the procedures and/or methods proposed by the present invention. The memory 114 is connected to the processor 112 and stores various types of information related to operations of the processor 112. The RF unit 116 is connected to the processor 112 and transmits and/or receives RF signals. The UE 120 includes a processor 122, a memory 124 and an RF unit 126. The processor 122 may be configured to implement the procedures and/or methods proposed by the present invention. The memory 124 is connected to the processor 122 and stores various types of information relating to operations of the processor 122. The RF unit 126 is connected to the processor 122 and transmits and/or receives RF signals. The BS 110 and the UE 120 may have a single antenna or multiple antennas.

The embodiments of the present invention described hereinbelow are combinations of elements and features of the present invention. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present invention may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present invention may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment. It will be obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present invention or included as a new claim by subsequent amendment after the application is filed.

In the embodiments of the present invention, a description is given, centering on a data transmission and reception relationship between a BS and a UE. In some cases, a specific operation described as performed by the BS may be performed by an upper node of the BS. Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with an MS may be performed by the BS, or network nodes other than the BS. The term ‘eNB’ may be replaced with the term ‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc. The term ‘UE’ may be replaced with the term ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’, ‘mobile terminal’, etc.

The embodiments of the present invention may be achieved by various means, for example, hardware, firmware, software, or a combination thereof. In a hardware configuration, the methods according to the embodiments of the present invention may be achieved by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.

In a firmware or software configuration, the embodiments of the present invention may be implemented in the form of a module, a procedure, a function, etc. For example, software code may be stored in a memory unit and executed by a processor. The memory unit is located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present invention may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the present invention. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by the appended claims and their legal equivalents, not by the above description, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a UE, a BS or other devices of a wireless communication apparatus. Specifically, the present invention can be applied to a method for transmitting uplink control information and a device for the same. 

The invention claimed is:
 1. A method for reporting channel state information (CSI) at a User Equipment (UE) in a wireless communication system, the method comprising: configuring a CSI report set including a first serving cell and a second serving cell, wherein each serving cell comprises a plurality of independently configured subframe subsets; receiving, in a predetermined subframe, a physical downlink control channel (PDCCH) signal requesting an aperiodic CSI report on the CSI report set; and transmitting a physical uplink shared channel (PUSCH) signal including first CSI on the corresponding subframe subset in the first serving cell and second CSI on the corresponding subframe subset in the second serving cell, wherein, if the PDCCH signal includes a 1-bit subframe subset indicator, at least one of the first CSI and the second CSI is calculated based on a subframe subset indicated by the subframe subset indicator.
 2. The method according to claim 1, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the predetermined subframe belongs to different subframe subsets in the CSI report set, the first CSI and the second CSI are calculated based on a same subframe subset as a subframe subset to which the predetermined subframe belongs in a serving cell in which the PDCCH signal is received.
 3. The method according to claim 1, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the PDCCH signal is received in the first serving cell, the first CSI is calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI is calculated based on a subframe subset different from the subframe subset to which the predetermined subframe belongs in the first serving cell.
 4. The method according to claim 1, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the PDCCH signal is received in the first serving cell, the first CSI is calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI is calculated based on the subframe subset indicated by the subframe subset indicator.
 5. The method according to claim 1, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the PDCCH signal is received in the first serving cell, the first CSI is calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI is calculated based on a subframe subset different from a previously reported subframe subset.
 6. A communication device configured to report channel state information (CSI) in a wireless communication system, the communication device comprising: a radio frequency (RF) unit; and a processor, wherein the processor is configured to configure a CSI report set including a first serving cell and a second serving cell, each serving cell including a plurality of independently configured subframe subsets, to receive, in a predetermined subframe, a physical downlink control channel (PDCCH) signal requesting an aperiodic CIS report on the CSI report set, and to transmit a physical uplink shared channel (PUSCH) signal including first CSI on the corresponding subframe subset in the first serving cell and second CSI on the corresponding subframe subset in the second serving cell, and wherein, if the PDCCH signal includes a 1-bit subframe subset indicator, at least one of the first CSI and the second CSI is calculated based on a subframe subset indicated by the subframe subset indicator.
 7. The communication device according to claim 6, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the predetermined subframe belongs to different subframe subsets in the CSI report set, the first CSI and the second CSI are calculated based on a same subframe subset as a subframe subset to which the predetermined subframe belongs in a serving cell in which the PDCCH signal is received.
 8. The communication device according to claim 6, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the PDCCH signal is received in the first serving cell, the first CSI is calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI is calculated based on a subframe subset different from the subframe subset to which the predetermined subframe belongs in the first serving cell.
 9. The communication device according to claim 6, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the PDCCH signal is received in the first serving cell, the first CSI is calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI is calculated based on the subframe subset indicated by the subframe subset indicator.
 10. The communication device according to claim 6, wherein, if the PDCCH signal does not include a 1-bit subframe subset indicator and the PDCCH signal is received in the first serving cell, the first CSI is calculated based on a subframe subset to which the predetermined subframe belongs in the first serving cell and the second CSI is calculated based on a subframe subset different from a previously reported subframe subset.
 11. A method for reporting channel state information (CSI) at a User Equipment (UE) in a wireless communication system, the method comprising: configuring a CSI report set including a first serving cell and a second serving cell, wherein each serving cell comprises a plurality of independently configured CSI subsets; receiving, in a predetermined subframe, a physical downlink control channel (PDCCH) signal requesting an aperiodic CSI report on the CSI report set; and transmitting the aperiodic CSI report including a first CSI of the first serving cell or a second CSI of the second serving cell via a physical uplink shared channel (PUSCH) signal, wherein if the PDCCH signal includes an indicator field, at least one of the first CSI and the second CSI is calculated based on a CSI subset indicated by the indicator field. 